The role of distributed and segregated synaptic clusters in the olfactory bulb

The specific spatial organization of olfactory bulb network elements and their synaptic connectivity has evolved in such a way to subserve special computational functions needed for odor detection and recognition, but which are still largely unknown. A particularly intriguing example of this organization is the spatially distributed and segregated synaptic clusters, experimentally observed in the olfactory bulb, that often take the form of cellular columns with preferential connectivity in a spatially restricted region below a glomerulus. Understanding the neural basis of odor processing therefore requires understanding the computational functions and role of glomerular units, and how they interact with each other to modulate the input/output (I/O) processing occurring in the olfactory bulb. To address these problems, we used a model with a realistic three dimensional (3D) representation of overlapping and interacting dendrites of mitral and granule cells. With this model, we have been able to obtain new findings that are not obtainable with experiments or simpler artificial models, and make several experimentally testable predictions. In particular, we have found that column formation is an activity-dependent process, whose main functional role is to regulate the spread of activity out of a glomerulus; that columns interact, positively or negatively, in a distancedependent manner; and that sequential odor exposure produces non-commutative processing. Finally, we introduce the concept of “odor operator”, defined as the overall interaction between mitral cells belonging to the same or different glomerular units, and show how it can be developed into a promising theoretical framework for insight into the neural basis of olfactory processing.